High voltage three phase transformer



1966 w. w. RENBERG, JR 3235823 HIGH VOLTAGE THREE PHASE TRANSFORMER Filed April 5, 1961 4 Sheets-Sheet 1 gxidtorng/ 1966 w. w. RENBERG, JR 3,235,823

HIGH VOLTAGE THREE PHASE TRANSFORMER Filed April 5. 1961 4 Sheets-Sheet 2 IN VEN TOR. ZV'ZZ/am Miter Renery (/7 fittorng BY LWM Feb. 15, w RENBERG, JR

HIGH VOLTAGE THREE PHASE TRANSFORMER Filed April 5., 1961 4 Sheets-Sheet 3 INVENTOR. I j; MZZ/am Z/aer Rezzfiery (/2 BY it Feb. 15, 1966 1 w, w, RENBERG, JR 3,235,823

HIGH VOLTAGE THREE PHASE TRANSFORMER Filed April 5. 1961 4 Sheets-Sheet 4.

INVENTOR- MZZ/am Z/alter P627662; (/2? BY no M flaw/nay United States Patent 3,235,823 HIGH VOLTAGE THREE PHASE TRANSFORMER William Walter Renberg, Jr., Bridgeville, Pa, assiguor to McGraw-Edison Company, Milwaukee, Wis, a corporation of Delaware Filed Apr. 3, 1961, Ser. No. 100,357 14 Claims. (Cl. 33612) This invention relates to stationary induction apparatus and in particular to a three-phase electrical power transformer and its method of construction.

The kva. rating of threeaphase electrical power transformers is limited by the road clearances and weight limatations of flatbed, depressed center, and Schnabel railroad cars used in transporting the transformer from the factory to the site where it is to be installed. Shipping limitations of railroad cars have prevented the increase in voltage and kva. rating of three-phase transformers demanded by the ever-expanding electrical power systems. Flat cars and Schnabel cars are only available in capacities up to 500,000 pounds, and depressed-center cars, used when very tall transformers must be shipped, have less capacity than flat cars. The Railway Line Clearances list the published clearances and weight limitations for railroads in the United States.

In order to maintain the physical dimensions of extrahigh voltage, three-phase transformers, e.g., 345 kilo-volts and above, within road clearances and also provide adequate clearance to prevent breakdown between high voltage parts, it has heretofore been necessary to tilt the high voltage bushings excessively and to locate them at undesirable positions wherein they are not symmetrically arranged relative to the corresponding phase coils. Although shell type construction is preferable for extrahigh voltage, three-phase power transformers, it is difiicult to construct a conventional three phase shell type transformer having adequate clearances for use at 345 kilovolts and higher ratings. Certain localities are so inaccessible that it is impossible to ship prior art lange kva. rating three-phase transformers thereto, and consequently it has been necessary to use single-phase transformers in a three-phase bank instead.

It is an object of the invention to provide a three-phase electrical power transformer which weighs considerably more than the capacity of available railroad cars but can be readily shipped from factory to installation site.

It is a further object of the invention to provide a threephase electrical power transformer having physical dimensions of greater magnitude than the published clearance limitations for railroads but which can be readily shipped from factory to destination point.

It is a further object of the invention ot provide an improved three-phase electrical power transformer and its method of construction wherein it is unnecessary to tilt the high voltage bushings excessively to obtain adequate clearances even for ratings above 345 kilovolts and wherein the high voltage bushings may be positioned directly above the corresponding phase coils.

Still another object of the invention is to provide an improved three-phase shell type electrical power transformer and method of construction therefor having adequate clearances to prevent electrical breakdown even in ratings above 345 kilovolts.

Another object of the invention is to provide a threephase electrical power transformer which can be shipped to inaccessible locations even in large kva. ratings.

A further object of the invention is to provide an improved zthree-phase electrical power transformer and its method of construction which eliminates the costly, heavy current, low voltage, isolated phase bus duct interconnections required when three single-phase, main step-up transformers are connected in a three-phase bank.

It is still another object of the invention to provide an improved three-phase power transformer which can utilize the simpler and more efiicient insulation structure as well as the superior physical strength and clamping characteristics inherent in .a shell type transformer, in comparison to a core type, at extra-high voltages and high kva. ratings.

These and other objects and advantages of the invention will be more readily apparent from the following detailed description when taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a front view of a preferred embodiment of the invention;

FIG. 2 is a top view of the embodiment of FIG. 1;

FIG. 3 is a vertical sectional view taken along line 3-3 of FIG. 1;

FIG. 4 is a partial view showing a temporary shipping cover assembled on a lower tank portion of the embodiment of FIG. 1;

FIG. 5 is a perspective view of the embodiment of FIG. 1 with the tank covers of two of the phases broken away to illustrate typical three-phase transformer internal connections including the low voltage bus arrangement and three-phase tap changer suspended within the upper tank section;

FIG. 6 is a detail view of flange means for interconnecting portions of the casing of the embodiment of FIG. 1; and

FIG. 7 is a detail view illustratnig means for operating the three-phase tap changer of the embodiment of FIG. 1 from the exterior of the casing.

Referring to the drawing, the preferred embodiment of three-phase electrical power transformer of the invention includes a closed tank having three aligned, horizontally spaced apart lower tank portions A, B, and C interconnected by an upper tank section D disposed vertically above the three lower portions. The three lower tank portions A, B, and C are preferably supported on a single concrete pad 10. Each lower tank portion A, B, and C houses a shell type transformer core and coil assembly 11 for one of the phases of the power system. Each lower tank portion A, B, and C includes a base tank section 13 and a center tank section 14 vertically superimposed above and welded to base section -13. The core and coil assemblies 11, base tank sections 13, and central tank sections .14 are similar to the construction disclosed and claimed in the copending application Serial No. 24,429, now Patent No. 3,082,391, entitled Shell Type Trans-former in the name of Alexander Chiki and having the same assignee as this application.

In accordance with the preferred embodiment of the invention the three lower tank portions A, B, and C and the upper tank section D are shipped separately from factory to destination. The three lower tank portions A, B, and C are similar and only lower portion A will be described. Base section 13 of lower tank portion A provides shelf support for the corresponding phase core and coil assembly 11. Steel base section 13 is generally boxlike in external configuration and is open at the top. An outwardly extending horizontal flange 16 extends around the entire periphery at the open end of base section 13. Base section 13 includes a heavy bottom plate 18 having welded thereto upwardly extending front and rear walls 19 and upwardly extending end walls 20 joined by welding to the front and rear walls 19. Horizontally extending plates 22 welded to the top of the front and rear Walls 19 and to the top of the end walls 20 define the peripheral flange shelf 16. Horizontally spaced apart, vertically extending ribs 23 welded to and integral with the bottom plate 18, with the front, rear, and end walls 19 and 20, and with the plates 22 provide additional support for the horizontal shelf flange 16. Suitable lift lugs 24 are provided at each corner of the base section 13 so that the complete lower tank portion A can be handled readily with cable slings, chains, hooks, or jacks. If desired for self-cooled, forced-air cooled units, oil-distributing manifolds (not shown) are built as part of the base section 13.

Core and coil assembly 11 for phase A includes a rectangular, shell type winding 25 positioned in base section 13. Phase winding 25 is spaced above the bottom plate 18 by insulating blocks 27. Phase winding 25 comprises a plurality of coils 28 (see FIG. in vertical planes transverse of base section 13. Rectangular phase winding 25 has a window 29 adapted to receive core laminations 31 and is provided with vertical cooling ducts by spacers (not shown) between coils 28.

Core and coil assembly 11 for phase A also includes a magnetic core 33 formed by magnetic steel yoke and leg laminations 31 assembled with phase winding 25 and defining two abutting, closed, magnetic core portions 33a and 33b linking the winding 25. The stacked laminations 31 are supported on the peripheral shelf flange 16 and on an inverted T-beam 34 which extends through the window 29 and is supported at its ends on the flange 16. The T-bearn 34 supports the center leg of the core 33 formed by the abutting sides of the core portions 33a and 33b. Core supporting and insulating pads 36 are disposed between the laminations 31 and the shelf flange 16 and also between the T-beam 34 and the laminations 31. Magnetic'core 33 is preferably cooled by horizontal ducts formed by insulating spacers 37 inserted at vertically spaced apart points in the stack of laminations 31 and also by core-edge cooling vertical ducts formed by horizontally spaced apart, vertical insulating spacers 38 inserted between the core 33 and the walls of center tank section 14.

After the core laminations 31 are stacked, most of the weight of the winding 25 is carried from above by the core 33 which rests upon the peripheral flange 16 on the tank base section 13. After assembly of core laminations 31 on base section 13. the box-like central tank section 14 open at top and bottom is lowered over the magnetic core 33 and welded to base section 13. Central tank section 14 fits snugly over core 33 formed by the stacked laminations 31 and has a horizontally extending peripheral flange 40 at the lower end thereof which rests upon and is welded to base section peripheral flange 16 adjacent the outer margin thereof.

Central tank and clamping section 14 is provided with a channel-cross-section internal brace 41 around the entire periphery adjacent the upper end thereof. The core laminations 31 are clamped to base section 13 by a plurality of closely spaced jack screws 43 built into the internal bracing band 41 around the top of the central tank section 14 and which distribute the clamping pressure uniformly along the magnetic core 33. Holes 44 at spaced apart points in the upper wall of the internal brace 41 alford access to the jack screws 43. Each jack screw 43 includes an adjusting stud 45 engaged within a threaded hole in a plate 46 welded to internal brace 41 adjacent the bottom wall thereof. The lower end of adjusting stud 45 is afiixed to a nut 49 welded to a flat pressure plate 50 disposed above sheet insulating material 52 which rests upon the top core laminations 31 and helps distribute the load from the pressure plate 50 to the core 33. Turning of adjusting stud 45 advances pressure plate 50 toward, or withdraws it away from, base section 13 and thus provides controlled-pressure clamping of the core laminations 31 against the horizontal peripheral flange 16. Since the closely spaced jack screws 43 are entirely responsible for clamping, pressure at all points along the core periphery can be adjusted independently. Further, since the jack screws 43 in central tank section clamp the laminations 31 against base section 13 independent of the upper tank section D, it will be apparent that the lower tank portion A including core 4 and coil assembly 11 can be shipped from factory to destination without upper tank section D.

A nut 53 on adjusting stud 45 above plate 44 permits locking of adjusting stud 45 at the desired clamping pressure. A core pressure bearing pad 54 of suitable insulating material such as wood inserted between the top core laminations 31 extending through window 29 and the internal margin of the rectangular coils 28 wedges the winding 25 tightly against core 33. A horizontal flange 55 extends around the periphery of central section 14 at the upper end thereof. Spaced apart vertical ribs 56 welded to the flanges 40 and 55 and to the front, rear, and end walls of the center tank section 14 provide additional strength.

In accordance with the preferred embodiment of the invention, the three lower tank portions A, B, and C, each including base section 13, central section 14, and core and coil assembly 11, are assembled at the factory and shipped separately to the installation site. The low voltage bus bar leads 120, the tap leads 84, and the high voltage bushing leads from the windings 25 are provided with suitable terminal lugs 122, 85, and 126 respectively so that they can easily be connected in the field to the corresponding components within the upper tank section D. As explained hereinbefore, the core 33 is clamped to the base section 13, and wedging and blocking keep the windings 25 tightly in place. While being shipped from factory to destination, each lower tank portion A, B, and C is preferably assembled with a separate shipping cover 57 (see FIG. 4). Before shipment the lower tank portions A, B and C are dried out with great care by circulating air, having both its temperature and humidity precisely controlled, through the ducts of the windings 25 and core 33 as well as over the outer surfaces. While still warm all jack screws 43 and clamps are retightened to compensate for shrinkage and locked. If the lower tank portions A, B, and C are to be shipped with oil, each lower tank portion A, B, and C is immediately sealed after drying to prevent entrance of moist air and is then vacuum-filled with de-aerated, dry oil. Shipping cover 57 having a continuous gasket 58 around the periphery thereof is then immediately bolted to the horizontal flange 55 at the upper end of the central tank section 14 to prevent absorption of moisture by the oil during shipment.

If the lower tank portions A, B, and C are shipped without oil, it is preferred to fill them with nitrogen at a small positive pressure, after the temporary shipping cover 57 with sealing gasket 53 has been bolted in place, to prevent entrance of moisture during shipment.

It will be appreciated that the lower tank portions A, B, and C are only approximately two thirds the height of the final transformer casing and that shipping the lower tank portions A, B, and C and the upper tank section D separately permits the lower tank portions to be much taller and heavier, while remaining within clearance and weight limitations for railroads, than a conventional one-piece three-phase transformer wherein upper, central, and base sections are integral.

Preferably upper tank section D is shipped separately from the lower tank portions A, B, and C and is assembled thereto at the installation site. Upper tank section D includes all of the internal construction of the three-phase transformer including tap changer, bus bar assembly, and interphase connections. Upper tank section D is generally in the shape of an elongated box and is rectangular in transverse cross section. Upper tank section D has three Openings 60A, 60B, and 60C in the bottom thereof which mate with the open upper end of the center tank section 14 of the three lowertank portions A, B, and C.

Although the upper tank section D may be of one piece construction, in the preferred embodiment upper tank section D comprises three integrally-united covers 61A, 61B, and 61C. Each cover 61 is generally box;

assasss like in shape and has one of the openings 60 at the lower end. Each cover 61 includes opposed front and rear Walls 62, opposed end walls 63, and a top wall 64. Preferably a box-section brace 65 extends around the periphery of each cover 61 at the lower end of the front and rear walls 62 and end walls 63, and the lower wall of the brace 65 is extended to form a horizontal flange 66 which mates with, and in the final assembly is welded to, flange 55 on center tank section 14. Preferably brace 65 is formed into compartments (not shown) which provide additional space for gas expansion.

Covers 61A and 61C on end lower tank portions A and C narrow to throat portions 68A and 680 on the end thereof adjacent the middle lower tank portion B, and cover 61B on middle lower tank portion B narrows to throat portions 68B and 68B on the ends thereof. Each throat portion 68 is approximately rectangular in cross section and terminates in a peripheral flange 69 disposed in a vertical plane. Peripheral flange 69A on cover 61A mates with one flange 69B on cover 6113; similarly peripheral flange 69C on cover 61C mates with the other flange 69B on cover 6113.

The covers 61A, 61B, and 61C may be welded or bolted together in the final transformer. In the embodiment illustrated in FIGS. 1-3 the mating flanges 69A and 69B and the mating flanges 69B and 690 are welded together in the factory, and the integral covers 61A, 61B, and 61C forming upper tank section D are shipped as a single piece. In other embodiments the mating flanges 69A and 69B and the mating flanges 69B and 690 are united by bolt means (not shown) in the factory before shipment with continuous peripheral gasket means compressed between the flanges. In either method of construction, the three lower tank portions A, B, and C and three covers 61A, 61B, and 61C are temporarily gasketed and bolted or clamped together in the factory before shipment to assure accurate fit and for pressure testing of welds. The entire three-phase tank is completely sealed and pressure-tested in the factory. Preferably the tank is filled with oil and kept under hydrostatic pressure for several hours at the factory to detect leaks. The lower tank portions A, B, and C and the upper tank section D including integral covers 61A, 61B, and 61C are shipped separately from factory to destination. Suitable shipping covers (not shown) are bolted to the horizontal peripheral flange 66 on covers 61A, 61B, and 61C during shipment to prevent entrance of moisture into upper tank section D through the openings 60A, 60B, and 60C. At the installation site the three lower tank portions A, B, and C are installed on a single concrete slab using a suitable template to insure proper location of the three lower tank portions A, B, and C relative to the upper tank section D. In the embodiments wherein the covers 61A, 61B, and 61C are not welded together in the factory, the bolts uniting covers 61A61B61C permit adjustment for misalignment between the lower tank portions A, B, and C and the covers 61A, 61B, and 61C forming upper tank section D.

FIG. 6 illustrates an embodiment of the invention wherein the covers 61A, 61B, and 61C are not united for shipment but rather are transported with suitable shipping covers 72 shown in dotted lines bolted to the flanges 69A, 69B, 69B and 69C With continuous gaskets 73 disposed in peripheral grooves 74 in the flanges 69 and compressed between shipping covers 72 and flanges 69 to prevent entry of moisture into the tank covers 61 during shipment. At the installation site a peripheral collar 76 of U-shaped cross section enclosing the mating flanges 69A and 69B and surrounding the throat portions 68A and 68B is welded to the throat portions 68A and 68B to assure a leak-proof joint therebetween. A similar collar 76 enclosing the mating flanges 69B and 69C (not shown) and surrounding the mating throat portions 68B and 68C is similarly welded at the installation site to the throat portions 63B and 68C to assure a leak-proof seal therebetween. In all embodiments wherein upper tank section D is shipped separate from the lower tank portions A, B, and C, suitable shipping covers (not shown) are bolted to the horizontal peripheral flange 66 on covers 61A, 61B, and 61C with a gasket compressed therebetween during shipment to prevent entrance of moisture through openings 60A, 60B and 60C into the upper tank section D.

If the size of the three-phase transformer permits shipping of the separate single-phase portions, the covers 61A, 61B and 61C may be joined to the lower tank portions A, B, and C by welding the flanges 66 to the flanges 55 on the central tank selections 14- in the factory before shipment. In this embodiment wherein complete single-phase portions are shipped separately, the covers 61A, 61B, and 61C are not integral during shipment, and shipping covers 72 are bolted to the cover flanges 69A, 69B and 69C with gaskets 73 compressed within grooves 74 during shipment as shown in FIG. 6. Similarly, the three tank covers 61A, 61B, and 61C may be shipped separately with shipping covers bolted to the flanges 66 and 69, and the tank covers 61A, 61B, and 61C are then integrally united in the field by collars 76 welded to the throat portions 68 to form the upper tank section D.

The tank covers 61 having mating throat portions 68 integrally secured together define an elongated hollow compartment 77 lengthwise of the upper tank section D which communicates with the interior of the lower tank portions A, B, and C. The low voltage bus bars 110, the three-phase tap changer 78, interphase leads, and other three-phase transformer internal connections extend lengthwise of compartment '77 which contains a cooling and insulating liquid dielectric 137. The bridging reactors of the load tap changing equipment, the Y-delta terminal board, and other optional components of the three-phase transformer omitted from the drawing may also be positioned in the compartment 77.

The three-phase tap changer '78 is preferably of the positive-positioning type having in each phase a Geneva gear 79 of suitable insulating material adapted to drive a rotatable metallic contact 80 into sequential engagement with a plurality of stationary metallic contacts 82 arranged in a circle and electrically connected to tap leads 84 from the high voltage coils of the corresponding phase winding 25. The tap leads 84 are provided with suitable terminal lugs 85 (seen only in FIG. 4) so they may easily be connected to the stationary contacts 82 of the tap changer 78 after upper tank section D is positioned above the three lower tank portions A, B, and C. Geneva pinions 87 of suitable insulating material mounted on a common insulating shaft 88 extending longitudinally through compartment 77 are adapted to actuate the three Geneva gears 79. Insulating shaft 88 preferably comprises three sections 88A, 88B and 88C interconnected by suitable flexible couplings 89 to compensate for any misalignment between tank covers 61A, 61B, and 61C. The Geneva pinions 87 are displaced thirty degrees apart so that the movable contacts 80 are actuated successively and the torque required to actuate the three-phase tap changer '78 is minimized.

The stationary contacts 82 for each of the phases are mounted in a circle upon an insulating plate 90. Insulating bolts 91 of resin-bonded, pressed wood extending axially through insulating sleeve support members 92 aflix plate to vertical insulating posts 95. The depending posts 95 may be threaded at their upper ends and screwed into internally threaded cup portions of metallic brackets 96 (see FIG. 3) secured by suitable means such as welding to the interior surface of the top wall 64 of tank covers 61.

All components of tap changer 73 except the contacts 80 and 82 are of insulating material. Operation of tap changer 78 is accomplished by one revolution of the elongated horizontally insulating shaft 88 which extends lengthwise of the compartment 77 in the upper tank section D. Shaft 88 preferably extends through a stuffing box (see FIG. 7) mounted on vertical end wall 63 of cover 61A. Spiral miter gears 102 within a gear box 103 mounted on cover end wall 63 transmit motion at right angles between shaft 88 and a vertical stub shaft 104. A sleeve coupling 105 atfixed to vertical stub shaft 104 has a releasable pin-and-slot connection to a vertical operating shaft 106 for tap changer 78. Operating shaft 106 terminates in an operating handle 107 supported on a mounting bracket 108 afiixed to a sidewall of center tank section 14 of lower tank portion A at ground level. Releasable coupling 105 permits connection between operating shaft 106 on center tank section 14 and vertical stub shaft 104 after upper tank section D has been positioned above and welded to the three lower tank portions A, B, and C.

The low voltage copper bus bars 110 connecting the secondary windings of the phase coils 25 are positioned within elongated compartment 77 and supported upon a framework of transverse members 111, longitudinal members 112, and vertical posts 113 of suitable insulating material such as dry maple wood. Additional creep distance is secured by overlapping pressboard channels 115 which surround the copper bus bars 110 where they pass through the transverse insulating supports 111. The transverse members 111, longitudinal members 112, and vertical posts 113 of the supporting framework are joined together by high strength, resin-bonded pressed wood bolts 116. The upper end of the vertical posts 113 may be affixed to angle brackets 117 (see FIG. 3) welded to the interior surface of the upper wall 64 of the covers 61 to suspend the low voltage bus work within transformer oil 137 in the elongated compartment 77 in upper tank section D.

Low voltage leads 120 from the phase windings 25 disposed at the open end of lower tank portions A, B, and C are provided with suitable terminal lugs 122 so that they may be easily bolted or otherwise connected to the copper bus bars 110 when upper tank section D is positioned above and welded to lower tank portions A, B, and C. Each copper bus bar 110 preferably includes a plurality of separate aligned pieces 110A, 110B, and 110C disposed within covers 61A, 61B, and 61C respectively and joined together within the mating throat portions 68 by flexible strap copper connectors 124 to compensate for any misalignment when the flanges 69A and 69B and flanges 69B and 690 are welded together as in the preferred embodiment, or when the collars 76 are welded to the throat portions 68 as illustrated in FIG. 6.

If the covers 61A, 61B, and 61C are shipped separately, or if the single-phase transformers having the covers already assembled thereto are shipped separately, the flexible strap connectors 124 are joined to the aligned bus bar pieces 110A, 110B, and 110C at the installation site.

The high voltage leads 125 from the phase windings 25 in the lower tank portions A, B, and C are provided with suitable terminal lugs 126 for connection to the high voltage bushings 127 in the field. Mounting flanges 129 and are provided on the upper wall 64 of the tank covers 61 for the high and low voltage bushings 127 and 128 respectively which are shipped separately and assembled at the installation site. Shipping covers (not shown) for the bushing mounting flanges 129 and 130 prevent entry of moisture into the tank covers 61 during transportation from factory to destination. Manholes in each cover 61 provide access to the interior of the three-phase transformer to make electrical connections between the leads 84, 120, and 125 from the windings 25 in the lower tank portions A, B, and C and the corresponding three-phase transformer components supported in upper tank section D.

After upper tank section D is disposed above and welded to the lower tank portions A, B, and C at the installation site, cooling and insulating dielectric liquid 137 such as de-aerated, dry transformer oil is introduced into the three-phase transformer tank until it fills the lower tank portions A, B, and C and the upper tank section D to a level above the tap changer 78, low voltage bus bars 110, and other three-phase transformer internal connections. A cushion of inert gas 138 such as dry nitrogen gas is provided within upper tank section D at a positive pressure above the oil 137 to protect the transformer oil 137 and insulation against deterioration caused by oxygen and moisture. The internal box-section brace 65 around the inner periphery of cover 61 is preferably interconnected by conduit 140 with the gas cushion 138 above the oil 137 and provides auxiliary gas expansion space. Pressure relief devices 144 of the type disclosed in US. Patent 2,904,616 to Koepke et al. mounted on the upper wall 64 of the covers 61A, 61B, and 61C limit internal pressure within the three-phase tank to a safe value and exhaust the interior of the tank to the atmosphere in the event of excessive pressure due to a failure within the transformer. Resealing of the pressure relief devices 144 is automatic and against a residual positive pressure of gas 138 and thus provides protection against the entrance of moisture and against secondary explosions resulting from oxygen entering the tank and creating an explosive gas mixture.

After the upper tank section D is disposed above and welded to the center tank sections 14 of the lower tank portions A, B, and C at the installation site, suitable heat exchangers 146 are mounted on the transformer tank. Preferably each single phase core and coil 11 is cooled by a plurality of heat changers 146 each of which is provided with an upper header 148 communicating with the interior of tank cover 61 and compartment 77 and a lower header 149 communicating with the interior of base tank section 13. Brackets 150 and 151 are provided on the center tank sections 14 and on the covers 61 respectively for mounting the heat exchangers 146 which are shipped separately from factory to installation site and affixed to mounting brackets 150 and 151 after the lower tank portions A, B, and C and the upper tank section D are welded together at the installation site. Outlet and inlet conduits 153 and 154 integral with and extending outwardly from the front and rear walls of the tank covers 61 and base tank sections 13 respectively are provided for connection in the field with the upper and lower headers 148 and 149 respectively at the installation site, and top and bottom isolating valves 155 and 156 are provided between the upper and lower headers 148 and 149 and the interior of the three-phase tank to isolate the cooling system from the tank and to permit the heat exchangers 146 to be installed in the field without the necessity of drawing the oil 137 from the threephase transformers. Self-cooled pumps 157 on the heat exchangers 146 circulate the oil 137 through the tubes of the oil-to-air heat exchanger, through the lower header 149 into the base tank section 13 and from there through the windings 25 and past the core 33 into the upper header 148.

The preferred embodiment of the invention illustrated in the drawing is of the forced-oil, forced-air cooling type which circulates the oil 137 through the tubes (not shown) of the oil-to-air heat exchanger 146 and transfers heat to radiating fins (not shown) which are cooled with air driven by fans 158 directed away from the transformer tank. It will be appreciated that inasmuch as the oil 137 is common to all three single-phase core and coil assemblies 11 and to heat exchangers 146 associated with each single-phase core and coil, the reliability of the three-phase transformer is increased in comparison to a bank of three separate single-phase transformers. If an individual heat exchanger 146 for one of the phases must be disconnected for repair or servicing, the heat exchangers 146 for the other two phases continues to cool the oil 137 by circulation through the heat exchangers 146 associated with the other two phases.

It will be appreciated that the disclosed apparatus, which allows separate shipping of portions of a threephase power transformer, permits construction of threephase transformers of considerably higher kva. rating than the prior art apparatus which necessitated one-piece shipment and was limited by published railroad weight and clearance limitations. The disclosed construction permits shipment from factory to installation of three-- phase power transformers considerably heavier than the 500,000 pound limit to which Schnabel and flatbed railroad cars are limited. Further, the disclosed apparatus permits construction of three-phase power transformers having physical dimensions considerably greater than the published clearance limitations for railroads. Inasmuch as the transformer height is not restricted by published clearance limitations, much more freedom is possible in the choice of the proportions of core and coil and economics in construction can be effected in comparison to prior art apparatus. Inasmuch as the length of the threephase transformer is not restricted by railroad shipping limitations, extra-high voltage three-phase units can be considerably longer than prior art construction. This permits mounting the primary bushings 127 so that they are not tipped excessively as required in prior art units to obtain adequate clearance to prevent breakdown. Further, the high voltage bushings 127 can be located directly above the corresponding phase winding 25, thus simplifying the lead structure and the problem of adequately insulating the high voltage line.

The disclosed construction permits shipment of threephase power transformer units to places which heretofore were too inaccessible to permit shipment thereto of singlepiece prior art units of the desired large kva. rating. In the event of failure of one phase winding of the disclosed three-phase transformer, it is only necessary to free the lower tank portion A, B, or C having the failed winding 25 from the upper tank section D and return it to the factory for repair instead of returning the entire three-phase transformer as in prior art one-piece construction. The disclosed transformer permits construction of three-phase units of the preferred shell form construction in voltages of 345 kilovolts and above whereas one-piece shell type construction presents great difliculties at such extra-high voltages due to the large clearances required to adequately insulate at 345 kilovolts and above.

It is believed shell type transformers are preferable to core type at 345 kilovolts and above because the shell type provides a simpler and more efiicient insulation structure to withstand such extra-high voltages. Further, transformers for voltages of 345 kilovolts and above commonly are high in kva. rating, and such high kva. capacity often results in physical size and weight of a one-piece unit which is impossible to transport over existing railway facilities and also increases the problems of provid ing the necessary physical strength and clamping to resist short circuit forces. It is believedthat shell type transformers are superior to core-type in providing the required physical strength and clamping to resist short circuit forces for high kva., extra-high voltage transformers. Furthermore, extra-high voltage transformers often incorporate the forced-oil system of cooling, and the vertical disposition of the coils of shell type transformers and the baffie inherently provided by the magnetic core thereof are ideally suited for use with forced-oil cooled units. Construction of shell form units having such superior characteristics presents great difiiculties in conventional onepiece, extra-high voltage transformers, whereas the disclosed invention greatly facilitates construction of such preferred shell f-orm units in voltages of 345 kilovolts and above.

The disclosed construction eliminates the costly, heavy current, low voltage, isolated phase bus duct interconnections required for a three-phase bank of individual single-phase, generator main step-up transformers. The

isolated phase bus ducts between single-phase transformers are expensive and make the typical delta connection between separate single-phase units costly and complex, and the subject construction wherein all low voltage bus bars are internally mounted within upper tank section D eliminates such costly isolated phase bus duct interconnections between single-phase units.

The embodiments of the invention which can be divided into individual phase units by separation at the flange portions 69 permits the necessary reserve capacity to be provided in a spare single-phase unit, which can be substituted for a damaged single-phase unit, rather than in a much more costly single-piece three-phase transformer.

Although the single embodiment has been illustrated and described to have aligned lower tank portions and an elongated upper tank section, it will be appreciated that the invention is not so limited and comprehends other arrangements such as an upper tank section in the shape of an equilateral triangle and the lower tank portions at the apices of the triangle or with the throat portions extending horizontally from the base sections or the center sections rather than from the covers.

While only a single embodiment of the invention has been illustrated and described, many modifications and variations thereof will be apparent to those skilled in the art, and consequently it is intended in the appended claims to cover all such modifications and variations thereof which fall within the true spirit and scope of the invention.

I claim:

1. A three-phase electrical power transformer comprising, in combination, a closed tank having three aligned, horizontally spaced apart, hollow, lower tank portions open at their upper end, each said lower tank portion having vertically superimposed, box-like base and center sections integrally welded together, said base section'being open at the top and having a horizontal shelf portion adapted to support a magnetic core, a magnetic core within said lower tank portion having laminations resting on said shelf portion, a single phase winding within said lower tank portion provided with taps and linking said core, said center section being open at the top and bottom and having a portion extending inwardly above said laminations and a plurality of adjustable means accessible from the interior of said center section and mounted in horizontally spaced apart relation on said inwardly projecting portion for exerting pressure vertically downward against said laminations to clamp said core against said shelf portion of said base section; an elongated, boxlike, hollow, upper tank section disposed above and covering said lower tank portions and having openings in the lower wall thereof each of which mates with the open end of said center section of one of said lower portions, said upper tank section being removable from said lower tank portions for shipment and being secured in fluidtight relation to said lower tank portions in operation, whereby said lower tank portions may be shipped separately with said magnetic core clamped against said shelf portion, a cooling and insulating dielectric fluid filling said base sections and said center sections and at least partially filling said upper section, means including first electrical conductor means extending horizontally through and mounted within said upper tank section above said three single phase windings and immersed in said fluid for connecting said single-phase windings in three-phase circuit relation during operation and being disconnectable for shipment, and a three-phase tap changer mounted within said upper tank section and having a common operating member extending longitudinally through said upper tank section and three sets of stationary contacts each of which is disposed directly above and connected by second conductor means to said taps on one of said singleaphase windings and immersed in said fluid within said upper tank section during operation, said second conductor means being disconnectable for shipment.

2. A three-phase electrical power transformer comprising, in combination, three aligned, horizontally spaced apart, hollow lower tank portions open at their upper ends, each lower tank portion having a horizontal shelf portion and vertical sidewalls between said shelf portion and said open upper end, a shell type single-phase core and coil assembly in each said lower tank portion surrounded by said sidewalls and including a pair of closed magnetic cores having laminations in horizontal planes supported on said shelf portion, means including members afiixed adjacent the upper end of said vertical sidewalls of said lower tank portions and extending inwardly above said lamination for clamping said laminations against said shelf, an elongated, hollow upper tank section positioned above and covering said lower tank portions and having three openings in the lower end thereof each complementary to the open end of one of said lower tank portions, said upper tank section being removable from said lower tank portions for shipment and being secured in fluid-tight relation to said lower tank portions in operation, whereby said lower tank portions may be separately shipped with said core and coil assembly clamped against said shelf portion, electrical conductor means mounted in said hollow upper tank section for connecting the single-phase coils in said lower tank portions in three-phase circuit relation during operation, and a cooling and insulating fluid filling said lower tank portions and at least partially filling said upper tank section, said conductor means being disconnectable from said single-phase coils for shipment.

3. A three-phase electrical power transformer comprising, in combination, a closed tank including three aligned, horizontally spaced apart lower tank portions, each lower tank portion including a box-like base section open at the top and having a horizontal shelf portion adapted to support a magnetic core, a box-like center section open at top and bottom and integrally secured to the open top of said base section, a magnetic core within said lower tank portion supported on said shelf portion, a single phase winding within said lower tank portion linked with said magnetic core, and means within said center section for clamping said magnetic core against said shelf portion; an elongated, hollow, box-like upper tank section disposed above and covering said lower tank portions and having three openings in the lower end thereof each complementary to the open top of the center section of one of said lower tank portions, said upper tank section being removable from said lower tank portions for shipment and being secured in fluid-tight relation to said lower tank portions in operation, whereby said lower tank portions may be separately shipped with said magnetic core clamped against said shelf portion, means including elongated metallic bus bars mounted and extending longitudinally within said hollow upper tank section above the single phase windings of all three lower tank portions for connecting said single-phase windings in said lower tank portions in three-phase circuit relation during operation, and a cooling and insulating fluid filling said lower tank portions and at least partially filling said upper tank section, said connecting means being disconnectable from said single-phase coils for shipment.

4. A three-phase electrical power transformer comprising, in combination, a closed tank including three aligned, horizontally spaced apart, hollow lower tank portions, each lower tank portion including vertically super-imposed, box-like base and center tank sections secured together in fluid-tight relation and a shell type single-phase core and coil assembly disposed therein, said base section being open at the top and having a horizontal shelf portion, the magnetic core of said assembly having laminations in horizontal planes resting upon said shelf portion, said center section being open at the top and bottom and having an internally projecting member integral therewith extending around the internal periphery thereof above said core laminations and a plurality of adjustable means accessible from the interior of said center section and mounted in horizontally spaced apart relation on said member for clamping said magnetic core laminations against said shelf portion, an elongated, hollow upper tank section disposed above and covering said lower tank portions and having three openings in the bottom thereof each complementary to the open top of one of said center sections, said upper tank section being removable from said lower tank sections for shipment and being secured in leak-proof relation to said lower tank portions in operation, whereby said lower tank portions may be separately shipped with said magnetic core laminations clamped against said shelf portion, an insulating and cooling fluid filling said lower tank portions and at least partially filling said upper tank section, and means including elongated metallic bus bars mounted and extending longitudinally within said upper tank section above said core and coil assemblies of all three lower tank portions and immersed in said fluid for interconnecting the single-phase coils within said lower tank portions in three-phase circuit relation during operation and being disconnectable therefrom for shipment.

5. A three-phase electrical power transformer comprising, in combination, a closed tank including three aligned, horizontally spaced apart lower tank portions, each lower tank portion including a box-like base section open at the top and having a horizontal shelf portion adapted to support a magnetic core, a box-like center section open at top and bottom and integrally secured to the open top of said base section, two closed magnetic cores having juxtaposed legs within said center section and laminaitons in horizontal planes supported on said shelf portion, a single-phase winding within said lower tank portion having coils disposed in vertical planes linked with said magnetic cores, and means including a member aflixed adjacent the open top of said center section and a plurality of adjustable means mounted in horizontally spaced apart relation on said member for clamping said laminations of said magnetic cores against said shelf portion; an elongated, hollow, box-like upper tank section disposed above and covering said lower tank portions, said upper tank section including three hollow box-like covers each disposed above one of said lower tank portions and having an opening in its lower end mating with and secured in fluid-tight relation to the open top of the center tank section of said one lower tank portion, during operation and being removable therefrom for shipment, whereby said lower tank portions may be separately shippedwith said magnetic core laminations clamped against said shelf portion, the end covers having hollow throat portions extending horizontally toward the middle cover and the middle cover having diametrically opposed, horizontally extending, hollow throat portions mating with and secured in fluidtight relation to said throat portions on said end covers, said covers joined together by said throat portions defining an elongated hollow passageway communicating with the interior of said lower tank portions, means including electrical conductors extending longitudinally through said hollow passageway above said single phase windings of all three lower tank portions for connecting said single-phase windings in three-phase circuit relation, and a cooling and insulating dielectric fluid filling said lower tank portions and at least partially filling said passageway.

6. A three-phase electrical power transformer comprising, in combination, a closed tank having three aligned, horizontally spaced apart, hollow, lower tank portions open at their upper ends, each lower tank portion having a peripheral horizontal shelf and sidewalls extending vertically upward from said shelf, a shell type single-phase core and coil assembly in each said lower tank portion surrounded by said sidewalls and including a pair of magnetic cores having adjacent legs and laminations in horizontal planes supported on said shelf and a winding having coils in vertical planes surrounding said adjacent legs and linked with said cores, means engaging said sidewalls adjacent said open upper end of each said lower tank portion for clamping said core laminations against said horizontal shelf, said close-d tank also having an elongated, hollow, upper tank section including three box-like covers each disposed above one of said lower tank portions and having an opening in the lower end complementary to and secured in fluid-tight relation to the open upper end of one of said lower tank portions, the end covers having hollow throat portions extending horizontally toward the middle cover and being open at their ends and having a peripheral flange at said open end, the middle cover having hollow throat portions extending horizontally from opposed sides thereof toward the throat portions on said end covers and being open at their ends and having peripheral flanges at said open end mating with said flanges on said end covers, means for securing said mating flanges on said end and middle covers together in fluid-tight relation, said covers joined together by said mating flanges defining a hollow elongated passageway communicating with the interior of said lower tank portions, a primary and a secondary bushing on each cover extending into said pasageway and having conductors extending therethrough, means including metallic bus bars extending longitudinally through said hollow passageway and extending above said three core and coil assemblies for electrically connecting said single-phase coils in three-phase circuit relation, each bus bar having three portions each of which is mounted within one of said covers and is disconnectable from the other portions for shipment, said bus bars being connected to said conductors extending through said secondary bushings, and a cooling and insulating dielectric fluid filling said lower tank portions and at least partially filling said passageway.

7. A three-phase electrical power transformer comprising, in combination, a closed tank having three horizontally spaced apart, hollow lower tank portions open at their upper end and an elongated, hollow upper tank section disposed above and covering said lower tank portions and having three openings in the lower end thereof each of which mates with and is secured in fluid-tight relation to the 'open end of one of said lower tank portions during operation and is removable therefrom for shipment, each said lower tank portion having a horizontal shelf portion and vertical walls between said shelf portion and said open upper end of said lower tank portion, a shell type single-phase core and coil assembly including a pair of magnetic cores having juxtaposed legs and laminations in horizontal planes supported on said shelf portion and a coil disposed in a vertical plane and surrounding said juxtaposed legs and having taps and linked with said cores disposed within each said lower tank portion, means within each lower tank portion for clamping said laminations against said shelf portion, said upper tank section defining a horizontal passageway communicating with the interior of said three lower tank portions, a three-phase tap changer in said passageway having three sets of stationary contacts each of which is disposed above and connected to said taps on one of said single phase coils, means including metallic bus bars extending horizontally through said passageway above said windings of all three of said single phase coils for connecting said single-phase coils in three-phase circuit relation, three high voltage insulating bushings each of which is mounted on said upper tank section above one of said single phase windings and has a conductor extending therethrough connected to said one single phase winding, a plurality of low voltage insulating bushings mounted on said upper tank section, at least one of said low voltage bushings being disposed above each core and coil assembly and having a conductor extending therethrough connected to one of said bus bars, and an insulating dielectric liquid filling said lower tank portions and at least partially filling said upper tank section.

8. A three-phase electrical power transformer comprising, in combination, three horizontally spaced apart, hollow, lower tank portions open at their upper end, each said lower tank portion including a box-like base section open at the top and having a horizontal shelf portion adapted to support a magnetic core, a shell type core and coil assembly including a pair of magnetic cores having juxtaposed legs and laminations in horizontal planes resting on said shelf portion and a single phase winding surrounding said juxtaposed legs and linked with said cores, and a box-like center section open at top and bottom and surrounding said core and coil assembly and integrally welded to said base section, said center section having an internal frame extending inwardly above said core laminations, said center section also having a plurality of adjustable means accessible from the interior thereof mounted in horizontally spaced apart relation on said frame for exerting pressure vertically downward against said core laminations to clamp said core against said shelf portion of said base section; a box-like, hollow upper tank section disposed above said lower tank portions and having three openings in the lower wall thereof each complementary to and mating with the open end of said center section of one of said three lower tank portions, said upper tank section being removable from said lower tank portions for shipment and being secured in fluid-tight relation to said lower tank portions in operation, whereby said lower tank portions may be separately shipped with said magnetic cores clamped against said shelf portion, said upper tank section defining a hollow passageway registering with the interior of said lower tank portions, a plurality of primary and a plurality of secondary insulating bushings mounted on said upper tank section and having conductors extending therethrough extending into said passageway, one of said primary and One of said secondary bushings being disposed above each of said core and coil assemblies, a cooling and insulating dielectric fluid filling said lower portions and at least partially filling said passageway, and electrical conductor means including a plurality of elongated metallic bus bars mounted within said upper tank section and extending longitudinally within said passageway above all three of said core and coil assemblies and immersed in said fluid for connecting said single-phase windings in three-phase circuit relation, said conductors extending through said secondary bushings being connected to said bus bars.

9. A three-phase electrical power transformer comprising, in combination, a closed tank including three aligned, horizontally spaced apart, box-like base sections open at the top and having a horizontal shelf portion adapted to support a magnetic core, three box-like center sections, each being open at the top and bottom and disposed above and integrally secured in fluid-tight relation to the open top of one of said base tank sections, and three box-like, hollow covers each of which is open at the bottom end and disposed above and secured in fluid-tight relation to the open top of one of said center tank sections, adjacent covers having mating, horizontally extending, hollow throat portions secured together in fluid-tight relation, said covers joined by said throat portions defining an elongated horizontal passageway communicating with the interior of said center sections and said base sections, an insulating and cooling dielectric fiuid filling said base sections and center sections and at least partially filling said passageway, a shell type single-phase core and coil assembly immersed in said fluid within each said center section including a pair of magnetic cores having adjacent legs and laminations disposed in horizontal planes supported on said horizontal shelf portion and a winding having primary coils provided with taps and secondary coils disposed in vertical planes surrounding said adjacent legs and linked with said magnetic cores, each center section having means for clamping said core laminations against said shelf portion, conductor means including elongated metallic bus bars disposed in said passageway and immersed in said fluid for connecting the single-phase coils in three-phase circuit relation, each said bus bar extending above all three core and coil assemblies and having three portions each of which is mounted in one of said covers and is disconnectable from the other portions for shipment, a three phase tap changer having an operating member extending through said passageway above all three core and coil assemblies and having three portions each of which is mounted in one of said covers and is disconnectable from the other portions for shipment, said tap changer having three sets of stationary contacts each of which is connected to said taps in said primary coil of the corresponding core and coil assembly, and primary and secondary insulating bushings mounted on each of said covers and having conductors extending therethrough into said passageway, said conductors extending through said secondary bushings being connected to said bus bars.

10. A three-phase electrical power transformer comprising, in combination, a closed tank having three horizontally spaced apart, hollow lower tank portions open at their upper ends and a hollow upper tank section positioned above and covering said lower tank portions and having three openings in the lower end thereof each of which registers with and is secured in fluid-tight relation to the open upper end of one of said lower tank portions in operation and is removable therefrom for shipment, said upper tank section defining a horizontal hollow passageway communicating with the interior of said three lower tank portions, an insulating and cooling dielectric fluid filling said lower tank portions and at least partially filling said horizontal passageway, a shell type single-phase core and coil assembly including primary and secondary coils disposed in vertical planes immersed in said fluid within each of said lower tank portions, means in each said lower tank portion for clamping said core and coil assembly therein independently of said upper tank section, whereby said lower tank portions may be separately shipped with said core and coil assemblies clamped in position, means including electrical conductor means immersed in said fluid within said hollow horizontal passageway and mounted in said upper tank section for connecting said single-phase coils in three-phase circuit relation and being d-isconnectable from said coils for shipment, and primary and secondary insulating bushings on said upper tank section extending into said passageway and having conductors extending therethrough, one primary bushing being disposed above each core and coil assembly and the conductor extending therethrough being connected to said primary coil, at least one secondary bushing being disposed above each core and coil assembly and the conductor extending therethrough being connected to said conductor means mounted in said upper tank section.

11. A three phase electrical power transformer comprising, in combination, a closed tank including three horizontally spaced apart, hollow, lower tank portions, each lower tank portion including vertically superimposed, box-like base and center tank sections integrally welded together and a single phase core and coil assembly including a pair of magnetic cores having juxtaposed legs and laminations in horizontal planes linked by coils disposed in vertical planes disposed therein, said base section being open at the top and having a horizontal shelf portion, the laminations of said magnetic cores resting upon said shelf portion, said center section being open at the top and bottom and having a plurality of horizontally spaced apart adjustable means accessible from the interior thereof for clamping said core against said shelf portion, said closed tank also including a hollow upper tank section disposed vertically above and covering said lower portions and having three openings in the bottom thereof each of which mates with and is secured in fluid-tight relation to the open end of said center section of one of said lower tank portions during operation and being removable therefrom for shipment, whereby said lower tank portions may "be separately shipped with said core clamped against said shelf portion, an insulating and cooling dielectric liquid filling said base and center sections and partially filling said upper section, a cushion of inert gas within said upper section above said liquid, a three-phase tap changer immersed in said liquid within said upper section and having three sets of stationary contacts each of which is connected to said taps on one of said single-phase windings, means including electrical conductors extending horizontally through said upper section and immersed in said liquid for connecting said single phase coils in three-phase circuit relation, and at least one externally disposed heat exchanger on each said lower tank portion having header means in communication with said liquid in said lower tank portion and in said upper tank section.

12. A three-phase electrical power transformer comprising, in combination, a closed tank having three aligned, horizontally spaced apart, hollow lower tank portions open at their upper end and each having a horizontal shelf portion and vertical sidewalls between said shelf portion and said open upper end, an elongated, hollow, upper tank section disposed above and covering said lower tank portions and having three openings in the lower 'end thereof each of which is complementary to the open upper end of one of said lower tank portions, said upper section being removable from said lower tank portions during shipment and secured in fluid-tight relation thereto during operation, said upper tank section defining a horizontal, hollow passageway registering with the interior of said lower tank portions, insulating and cooling fluid filling said lower tank portions and at least partially filling said passageway, a single-phase magnetic core and a singlephase coil having taps and linking said core within each of said lower tank portions and immersed in said fluid, said magnetic core having laminations in horizontal planes supported on said shelf portion, means including members in each lower tank section aflixed adjacent the upper end of said vertical sidewalls and extending inwardly above said laminations for clamping said laminations against said shelf portion, whereby said lower tank portions may be separately shipped with said magnetic cores clamped in position, means including horizontal first electrical conductor means suspended from said upper tank section within said passageway and immersed in said fluid for connecting said single-phase coils in three-phase circuit relation during operation, a three-phase tap changer mounted in said upper tank section and immersed in said fluid within said passageway and having a common operating shaft and three sets of stationary electrical contacts each of which is connected by second conductor means to said taps of one of said coils during operation, and at least one externally disposed heat exchanger on each of said lower tank portions having header means in communication with said fluid in said passageway and in said lower tank portion, said first and second conductor means being disconnectable for shipment.

13. A three-phase electrical power transformer comprising, in combination, a closed tank including three horizontally spaced apart, box-like, hollow base sections open at their top and having horizontal shelf portions adapted to support a magnetic core, three box-like, hollow center sections open at the top and bottom disposed above and integrally secured to said base sections, and an elongated box-like upper section disposed above and covering said center sections and having three openings in the bottom thereof each of which is complementary to the open upper end of one of said center sections, said upper tank section being removable from said center sections during shipment and secured in fluid-tight relation to said center sections during operation, an insulating fluid filling said base sections and center sections and at least partially filling said upper section, a shell type core and coil assembly including a pair of magnetic cores having juxtaposed legs and laminations in horizontal planes supported on each of said shelf portions and a single-phase winding having primary coils provided with taps and secondary coils in vertical planes surrounding said juxtaposed legs and linked with said cores and immersed in said fluid, each center section surrounding said core and coil assembly supported on said shelf portion and having means for clamping said core laminations against said shelf portion, electrical conductor means including elongated metallic bus bars mounted longitudinally Within said upper tank section and extending above said three core and coil assemblies and connected to said secondary coils and immersed in said fluid during operation for connecting said single-phase windings in three-phase circuit relation and being disconnectable from said windings for shipment, a three phase tap changer mounted Within said upper section and having a common operating member extending longitudinally through said upper section and three sets of stationary contacts each of which is connected by second conductor means to said taps on one of said secondary coils, said second conductor means being disconnectable for shipment, and primary and secondary insulating bushings on said upper section having conductors extending therethrough into the interior of said upper section and at least one primary and one secondary bushing being disposed above each said core and coil assembly and said conductors extending through said secondary bushings being connected to said bus bars.

14. A three-phase electrical power transformer comprising, in combination, a closed tank having an elongated, hollow, upper tank section and three aligned, horizontally spaced apart, hollow lower portions depending therefrom registering with the interior of said upper tank section, said upper section being removable from said lower portions during shipment and secured in fluid-tight relation to said lower portions during operation, an insulating and cooling fluid filling said lower tank portions and at least partially filling said upper tank section, each lower tank portion having a horizontal shelf portion and sidewalls extending vertically upwardly from said shelf portion, a pair of magnetic cores having juxtaposed legs and laminations disposed in horizontal planes supported on said shelf portion and a single-phase coil having taps and linking said magnetic cores disposed in each of said lower tank portions and immersed in said insulating fluid, means including members in each lower tank portion extending inwardly from said sidewalls above said laminations for clamping said l-aminations against said shelf portion, whereby said lower tank portions may be separately shipped with said magnetic cores clamped in position, a three-phase tap changer mounted within said upper tank section and immersed in said fluid and having three sets of stationary contacts each of which is connected by first conductor means to said taps on one of said single-phase coils during operation, said first conductor means being disconnectable during shipment, and second conductor means including elongated metallic bus bars mounted in and extending longitudinally of said upper tank section above all three of said single phase coils and immersed in said dielectric fluid for connecting said single-phase coils in three-phase circuit relation during operation, said second conductor means being detachable during shipment.

References Cited by the Examiner UNITED STATES PATENTS 2,085,080 6/1937 Brown 336-92 2,340,727 2/ 1944 Zelt 33668 X 2,915,720 12/1959 Mueller et al 36105 X 3,082,391 3/1963 Chiki 336210 FOREIGN PATENTS 847,774 6/ 1952 Germany.

JOHN F. BURNS, Primary Examiner.

JOHN F. COUCH, Examiner. 

10. A THREE-PHASE ELECTRICAL POWER TRANSFORMER COMPRISING, IN COMBINATION, A CLOSED TANK HAVING THREE HORIZONTALLY SPACED APART, HOLLOW LOWERTANK PORTIONS OPEN AT THEIR UPPER ENDS AND A HOLLOW UPPER TANK SECTION POSITIONED ABOVE AND COVERING SAID LOWER TANK PORTIONS AND HAVING THREE OPENINGS IN THE LOWER END THEREOF EACH OF WHICH REGISTERS WITH AND IS SECURED IN FLUID-TIGHT RELATION TO THE OPEN UPPER END OF ONE OF SAID LOWER TANK PORTIONS IN OPERATION AND IS REMOVABLE THEREFROM FOR SHIPMENT, SAID UPPER TANK SECTION DEFINING A HORIZONTAL HOLLOW PASSAGEWAY COMMUNICATING WITH THE INTERIOR OF SAID THREE LOWER TANK PORTIONS, AN INSULATING AND COOLING DIELECTRIC FLUID FILLING SAID LOWER TANK PORTIONS AND AT LEAST PARTIALLY FILLING SAID HORIZONTAL PASSAGEWAY, A SHELL TYPE SINGLE-PHASE CORE AND COIL ASSEMBLY INCLUDING PRIMARY AND SECONDARY COILS DISPOSED IN VERTICAL PLANES IMMERSED IN SAID FLUID WITHIN EACH OF SAID LOWER TANK PORTIONS, MEANS IN EACH LOWER TANK PORTION FOR CLAMPING SAID CORE AND COIL ASSEMBLY THEREIN INDEPENDENTLY OF SAID UPPER TANK SECTION, WHEREBY SAID LOWER TANK PORTIONS MAY BE SEPARATELY SHIPPED WITH SAID CORE AND COIL ASSEMBLIES CLAMPED IN POSITION, MEANS INCLUDIDNG ELECTRICAL CONDUCTOR MEANS IMMERSED IN SAID FLUID WITHIN SAID HOLLOW HORIZONTAL PASSAGEWAY AND MOUNTED IN SAID UPPER TANK SECTION FOR CONNECTING SAID SINGLE-PHASE COILS IN THREE-PHASE CIRCUIT RELATION AND BEING DISCONNECTABLE FROM SAID COILS FOR SHIPMENT, AND PRIMARY TANK SECTION EXARY INSULATING BUSHINGS ON SAID UPPER TANK SECTION EXTENDING INTO SAID PASSAGEWAY AND HAVING CONDUCTORS EXTENDING THERETHROUGH, ONE PRIMARY BUSHING BEING DISPOSED ABOVE EACH CORE AND COIL ASSEMBLY AND THE CONDUCTOR EXTENDING THERETHROUGH BEING CONNECTED TO SAID PRIMARY COIL, AT LEAST ONE SECONDARY BUSHING BEING DISPOSED ABOVE EACH CORE AND COIL ASSMEBLY AND THE CONDUCTOR EXTENDING THERETHROUGH BEING CONNECTED TO SAID CONDUCTOR MEANS MOUNTED IN SAID UPPER TANK SECTION. 